1. Field of the Invention
The present invention relates to an ultrasonic detecting apparatus, which is effective in inspecting defects on a surface joined by diffusion bonding.
2. Description of the Related Art
FIG. 28 shows an example of the structure of a furnace wall which is used in a plant or the like. This wall portion is a combination of a plurality of steel pipes 1 provided upright in parallel to one another with small distances therebetween and fins 2 provided between the individual steel pipes 1.
When damage 3 occurs in one of the steel pipes 1 and mending, such as bonding is required, it is difficult for a worker to access that portion of the damage 3 which faces towards the inside of the furnace because of the small distances between the steel pipes 1. To permit access to the damage not only from outside the furnace but also from inside, conventionally, welding was carried out after a scaffold 101 was set up inside the furnace as shown in FIGS. 29 and 30. Because putting up the scaffold 101 is time consuming, the mending takes a considerable time.
Conventionally, fusion welding in which a base metal 250 is cut into a V shape and padding is applied between the cut surfaces by welding has been common in bonding metal materials including iron and steel. A typical means for detecting a welding defect F at the padding is a P/S (Pulse Signal) probe type ultrasonic detecting apparatus which combines an ultrasonic transmitting element and an ultrasonic receiving element. As shown in FIG. 32, this ultrasonic detecting apparatus irradiates an ultrasonic wave perpendicular to the welded surface and receives the ultrasonic wave that returns through the same path, in order to detect a welding defect. The above fusion welding method requires several cutting processes and deforms the welded portion or thermally changes the composition. Securing a reliable welded portion with this method therefore requires highly skilled work and is costly.
Recently, there has been interest in the diffusion bonding method as one solution to the above problem. In this diffusion bonding method, an easily-diffusible thin metal sheet is positioned between the surfaces to be connected, and high temperature and pressure are applied to the portion near the surfaces to be connected in such a way that there is little plastic deformation, thereby diffusing atoms between the surfaces to be connected to accomplish bonding. Diffusion bonding has the advantages that it does not require any special skill and shows excellent performance, does not deform the outline of the connected surface and provides a connected surface with a uniform composition (see Japanese Unexamined Patent Application, First Publication No. 62-97784).
One metal-liquid phase diffusion bonding method which has been proposed is an amorphous bonding method which uses an amorphous sheet. This amorphous bonding method will now be discussed briefly with reference to the case where a steel pipe is bonded using an amorphous sheet containing boron which reduces the melting point. The amorphous sheet is a thin sheet made by rapid solidification and has a thickness of about 25 xcexcm.
First, an amorphous sheet whose composition is similar to that of a steel pipe (base metal) and which contains boron is inserted between the surfaces to be connected. Then, the amorphous sheet is heated to a temperature equal to or lower than the melting point of the base metal and equal to or higher than the melting point of the amorphous sheet. Consequently, boron in the amorphous sheet is diffused in the parent phase, lowering the melting point of the parent phase and melting the parent phase. When heating is maintained in that condition, further diffusion of boron lowers the concentration of boron. This raises the melting point of the parent phase, so that the parent phase is gradually solidified, thus achieving bonding.
This bonding method has several advantages, such as a shorter bonding time, a simpler connecting apparatus structure and a lower heating temperature as compared with the conventional welding.
An apparatus which implements this amorphous bonding method will be described briefly with reference to FIG. 31.
First, an amorphous sheet 72 is inserted between ends to be joined at the portion to be connected 34 of a steel pipe 1. Next, the upper and lower steel pipes 1 are held by a clamp (not shown) and are urged in the directions of the arrows so as to push together the portion to be connected 34. A high-frequency heating coil 104 heats the portion to be connected 34 which is under pressure from the clamp. The high-frequency heating coil 104 heats the portion to be connected 34 at a temperature equal to or higher than the melting point of the amorphous sheet 72 and equal to or lower than the melting point of the steel pipe 1. The aforementioned amorphous bonding is carried out in this way.
However, the conventional apparatus does not operate on the premise of bonding of one of a plurality of steel pipes 1 that are arranged with the small distances therebetween, as mentioned previously. That is, steel pipes can be bonded by this apparatus when sufficient working space can be provided around the steel pipes 1, whereas if a plurality of steel pipes 1. are arranged with small distances therebetween, sufficient working space cannot be secured around each steel pipe 1, and as a result, a high-frequency heating coil or the like cannot be set around the steel pipe 1.
As the joined or connected surface is formed perpendicular to the material surface according to the diffusion bonding method, an ultrasonic wave cannot be irradiated perpendicular to the connected surface for detecting a welding defect F in the connected surface formed by the diffusion bonding method. This disables the use of a P/S probe type ultrasonic detecting apparatus which combines an ultrasonic transmitting element and ultrasonic receiving element. One method which uses the conventional P/S probe type ultrasonic detecting apparatus has been proposed in, for example, Japanese Unexamined Patent Application, First Publication No. 6-63771. According to this method, as shown in FIG. 33, surfaces to be connected are so cut as to have certain angles and are butted so that an ultrasonic wave can be irradiated perpendicular to the connected surface. However, this method is not practical because it is difficult to cut the base metal.
Ultrasonic inspection of a connected surface formed perpendicular to the surface of the base metal can be carried out by a double-probe method which has an ultrasonic transmitting element and ultrasonic receiving element separately installed in two probes as shown in FIG. 34. This double-probe method uses an ultrasonic transmitting element and an ultrasonic receiving element separate from each other, reflects an ultrasonic wave inside the base metal to irradiate the ultrasonic wave on the connected surface at a predetermined angle, reflects the ultrasonic wave, reflected at the connected surface, in the base metal again and receives it at the receiving element.
However, the conventional double-probe method has a long propagation path for the ultrasonic wave in the base metal and uses multiple reflections which significantly attenuates the ultrasonic wave. What is more, because noise is occurs at every reflection, the sensitivity to detect minute defects is diminished. Those disadvantages make the conventional double-probe method impractical.
Accordingly, it is an object of the present invention to provide a connecting clamp, a connecting apparatus and a connecting method, which can allow a clamp section and heating member to be positioned around a rod member, such as a steel pipe, even if ample working space cannot be secured around the rod member. It is another object of this invention to provide an ultrasonic detecting method for inspecting a diffusion-bonded surface which has undergone simple material processing and which has a significantly improved defect detecting performance, and an apparatus which implements this method. It is a further object of this invention to provide an ultrasonic detector which is effective in inspecting a bonding defect at a diffusion-bonded portion of, particularly, a steel pipe.
A connecting clamp according to one aspect of this invention comprises a heating member which surrounds a portion to be connected of a rod member and heats the portion to be connected; and a first clamp section and a second clamp section positioned on opposite sides of the portion to be connected and clamping the rod member, whereby the portion to be connected is connected by heating the portion to be connected by the heating member while applying pressure to the portion to be connected by the first and second clamp sections, and is characterized in that the first and second clamp sections and the heating member are so arranged as to be slid around an outer surface of the rod member from one side of the rod member to the other side thereof. Note that the xe2x80x9crod memberxe2x80x9d includes a solid rod as well as a tubular member such as a steel pipe.
A connecting clamp according to another aspect of this invention, which connects a portion to be connected by heating it by means of a heating member, is characterized in that first and second clamp sections are so arranged as to be slid around an outer surface of the rod member from one side of the rod member to the other side thereof, the heating member has a heating coil so provided as to surround the rod member, the heating coil having a curved portion curved in one plane in such a way as to have an inside diameter slightly greater than an outside diameter of the rod member and an opening larger than the outside diameter.
In this case, it is desirable that each of the first and second clamp sections and the heating member should have a tubular shape and should comprise a plurality of components which are separable along the radial direction of the tubular shape. The number of separable components has only to be equal to or greater than two, and the separable components can have any size. The tubular shape may take any shape, such as a cylinder or a shape has a rectangular cross section, as long as it can surround a rod member.
It is further desirable that the first and second clamp sections and the heating member should have holding levers for respectively holding the first and second clamp sections and the heating member at the time of sliding the first and second clamp sections and the heating member around the outer surface of the rod member.
Further, it is desirable that the heating member should be further provided with a cooling pipe and a shield-gas feeding pipe, and each of the cooling pipe and the shield-gas feeding pipe should have a curved portion curved in one plane in such a way as to have an inside diameter slightly greater than the outside diameter of the rod member and an opening larger than the outside diameter.
The heating member may be constituted by stacking a plurality of shield-gas feeding pipes, a plurality of cooling pipes and a plurality of heating coils. In this case, as a plurality of shield-gas feeding pipes, a plurality of cooling pipes and a plurality of heating coils are stacked one on another, and they can be combined adequately in accordance with the condition of the portion to be connected of the rod member.
A connecting apparatus according to a further aspect of this invention comprises the above-described connecting clamp; a pressure applying means for applying pressure to the first and second clamp sections so as to urge them towards each other, and a power source for supplying power to the heating member.
A connecting method according to a still further aspect of this invention comprises a wax-material positioning stage of positioning a wax material between connecting ends at a portion to be connected of a rod member; a clamp-section attaching stage of positioning a first clamp section and a second clamp section on opposite sides of the portion to be connected and attaching the first and second clamp sections to the rod member; and a heating-member attaching stage of attaching a heating member in such a way as to surround the portion to be connected; and a connecting stage of connecting the portion to be connected by heating the portion to be connected by the heating member while applying pressure to the portion to be connected by the first and second clamp sections, the clamp-section attaching stage including a step of arranging the first and second clamp sections so as to be slid around an outer surface of the rod member from one side of the rod member to the other side thereof, the heating-member attaching stage including a step of arranging the heating member so as to be slid around the outer surface of the rod member from the one side of the rod member to the other side thereof.
The above-described connecting method of this invention is characterized in that the heating member is provided with a heating coil, a cooling pipe and a shield-gas feeding pipe, and each of the heating coil, the cooling pipe and the shield-gas feeding pipe having a curved portion curved in one plane in such a way as to have an inside diameter slightly greater than the outside diameter of the rod member and an opening larger than the outside diameter, and the heating-member attaching stage includes a stage of moving the heating coil, the cooling pipe and the shield-gas feeding pipe forward in such a way that said plane is approximately parallel to the upright-standing direction of the rod member to thereby guide the curved portions from a front side of the rod member toward a rear side thereof, and a stage of rotating said plane in such a way as to become perpendicular the upright-standing direction, so that the curved portions surround the portion to be connected.
It is desirable that the connecting stage should include a step of heating the rod member so that a distance between the connecting ends of the portion to be connected is decreased by thermal expansion of the rod member. Further, the wax-material positioning stage may include a step of positioning an insert member between the connecting ends and positioning the wax material between the insert member and each of the connecting ends.
According to a still further aspect of this invention, an ultrasonic detecting method using a double-probe method in which a transmitting element and a receiving element are separated from each other, directly irradiates an ultrasonic wave onto a surface to be probed inside a material at a predetermined angle, receives a reflected ultrasonic wave after being reflected inside the material once and performs probing while adequately changing the distance between the transmitting element and the surface to be probed and the distance between the transmitting element and the receiving element, whereby an internal defect present along the inspected surface perpendicular to the surface of the material can be detached.
As an apparatus which is used in this method, according to this invention, an ultrasonic detecting apparatus has been developed which comprises a transmitting element for emitting an ultrasonic wave towards a surface to be probed inside a sample from a surface of the sample at a predetermined angle; and a receiving element for receiving the ultrasonic wave reflected from the surface of the sample, the transmitting element and the receiving element being separated from each other on a single pedestal, wherein the transmitting element and the receiving element are movable on the surface of the sample in a direction perpendicular to the surface to be proved, and the distance between the transmitting element and the receiving element is arbitrarily changeable.
This ultrasonic detecting apparatus can be provided with a supplemental unit for ensuring efficient ultrasonic detection of a pipe member, such as a roller which is attached to the pedestal of the ultrasonic detecting apparatus so that the apparatus is movable around the pipe member, or a magnet which causes the ultrasonic detecting apparatus to be always attracted to a steel pipe and prevents the apparatus from coming off the steel pipe, at the time of inspecting the steel pipe, or an encoder attached to the pedestal so that the moving distance around the pipe member can be determined. To facilitate inspection of the outer surface of a pipe, the signal line of the probe and the signal line of the encoder may be made of a shape memory alloy which memorizes the same curvature as the pipe""s diameter.